Seat occupancy sensor unit for seat with spring suspension or seat pan

ABSTRACT

A pressure-responsive seat occupancy sensor unit ( 10 ) comprises a support plate ( 12 ) having a top surface ( 20 ) and a bottom surface, a plurality of spacer elements ( 14 ) defining an upper surface ( 18 ) of the pressure-responsive seat occupancy sensor unit, which upper surface the top surface of the support plate is arranged recessed from, a foam pad ( 22 ) disposed between the spacer elements on the support plate, a recess ( 24 ) formed in the top surface of the support plate, underneath the foam pad, and a pressure-responsive membrane switch ( 26 ) arranged in the recess. The recess has a depth exceeding the thickness of the pressure-responsive membrane switch. The foam pad is configured such that, upon it being compressed by application of pressure exceeding a certain threshold, it deforms so as to penetrate into the recess and activates the pressure-responsive membrane switch.

TECHNICAL FIELD

The present invention generally relates to sensing the occupancy stateof a vehicle seat. Specifically, the invention relates to apressure-responsive seat occupancy sensor unit for being placed on thebottom side of a seat cushion; i.e. between the seat cushion and thecushion-supporting means such as, e.g. a seat pan, springs etc.

BACKGROUND ART

Seat occupancy sensors are nowadays widely used in automotive vehiclesto provide a seat occupancy signal for various appliances, such as, e.g.a seat belt reminder, an auxiliary restraint system (airbag), etc. Seatoccupancy sensors exist in a number of variants, e.g. based oncapacitive sensing, deformation sensing or pressure (force) sensing.Pressure-sensitive seat occupancy sensors have typically been arrangedbetween the foam body of the seat cushion and the seat cover.

The possibility of customization and personalization of the vehicle bythe customer is a key selling factor of modern cars. This leads to manydifferent variants of car interiors being offered for one car model.With the increasing number of available options, severe constraintsarise concerning the implementation of technical equipment in thevehicle. With seat occupancy sensors arranged between the foam body ofthe seat cushion and the seat cover, every seat design (leather, cloth,sport, comfort, . . . ) requires specific development effort for theoccupant detection system. That induces high development costs andtherefore is an unattractive solution for the automotive industry. Aproblem to be solved is, therefore, to find a sensor solution, which isless influenced by seat design and thus can be used for a greatervariety of car seats or even car platforms.

Document DE 197 52 976 A1 discloses a vehicle seat occupancy sensor inthe shape of a film-type pressure sensor. The pressure sensor includes afirst carrier film, a spacer and a second carrier film, which aredisposed on one another in the manner of a sandwich. Contact elementsare arranged on the inner surfaces of the carrier films. An opening inthe spacer allows the contact elements to get into contact with eachother when pressure is applied on the sensor. The pressure sensor isarranged inside a cavity on the bottom side of the foam cushion of thevehicle seat. The pressure sensor is supported by a foam block, whichcloses the cavity and which rests on the seat pan.

Document DE 20 2010 003 563 U1 discloses a pressure-sensor unit,comprising a film-type pressure sensor. The pressure sensor includes twofilms maintained at a distance by a spacer material arranged therebetween. The pressure sensor is disposed on a compressible intermediatelayer, which is, in turn arranged on a base plate. Document JP 2011105278 discloses a seat occupancy sensor comprising a support plate withbearing elements for fixing the support plate on seat cushion suspensionsprings, wherein the bearing elements define an upper surface from whichthe top surface of the support plate is recessed. A foam pad carrying apressure-responsive detector is arranged between the bearing elements onthe support plate.

With pressure sensor units arranged on the B-surface of the seat cushion(i.e. on the side facing away from that on which an occupant may seathimself, between the seat cushion and the support thereof), the seatcushion transfers the pressure from the seating surface to the pressuresensor unit. As a matter of fact, the padding of the seat cushionbecomes part of the measurement unit. Whereas the production tolerancesof film-type pressure sensors may be controlled such that a uniformactivation pressure threshold (i.e. the pressure, at which the films ofthe pressure sensor get into contact with each other) is achieved forthe whole production, important investments would be necessary in theseat manufacturers' production in order to guarantee that the foam ofevery seat cushion has exactly the same thickness and behaves the sameway under pressure, in particular, transfers the same amount of pressureto the pressure-sensor unit.

BRIEF SUMMARY

The disclosure provides a pressure-responsive B-surface seat occupancysensor unit compatible with the production tolerances of vehicle seats.

A pressure-responsive seat occupancy sensor unit for detecting anoccupancy state of a seat, e.g. a vehicle seat, according to a firstaspect of the invention is configured for seats wherein the cushion issupported by springs. Such pressure-responsive seat occupancy sensorunit comprises a support plate having a top surface and a bottomsurface, a plurality of bearing elements for fixation of the supportplate on seat cushion suspension springs, the bearing elements definingan upper surface of the pressure-responsive seat occupancy sensor unit,which upper surface the top surface of the support plate is arrangedrecessed from, a foam pad disposed between the bearing elements on thesupport plate, a recess formed in the top surface of the support plate,underneath the foam pad, and a pressure-responsive membrane switcharranged in the recess. The recess has a depth exceeding the thicknessof the pressure-responsive membrane switch. The foam pad is configuredsuch that, upon it being compressed by application of pressure exceedinga certain threshold, it deforms so as to penetrate into the recess andactivates the pressure-responsive membrane switch.

As will be appreciated, due to the depth of the recess greater than thethickness (height) of the pressure-responsive membrane switch, there isan air gap between the pressure-responsive membrane switch and thebottom of the foam pad when the seat is in unloaded condition. The airgap thus prevents a so-called pre-loading of the pressure-responsivemembrane switch. Furthermore, if the foam pad deforms due to ageing andbegins sinking into the gap, it will not immediately apply a pre-load onthe membrane switch. Accordingly, a longer lifetime of the unit may beobtained.

Preferably, the bearing elements are integrally formed with the supportplate. The bearing elements and the support plate can be made from anysuitable material. Preferably, however, they are made frominjection-molded plastic.

According to a second aspect of the invention, the pressure-responsiveseat occupancy sensor unit is configured for seats wherein the cushionis supported by a seat pan (e.g. made from sheet metal or from plastic).The pressure-responsive seat occupancy sensor unit for detecting anoccupancy state of a seat according to the second aspect of theinvention comprises a support plate having a top surface and a bottomsurface, a plurality of spacer elements defining an upper surface of thepressure-responsive seat occupancy sensor unit from which upper surfacethe top surface of the support plate is arranged recessed from, a foampad disposed between the spacer elements, carried by the support plate,a recess formed in the top surface of the support plate, underneath thefoam pad, and a pressure-responsive membrane switch arranged in therecess. The recess has a depth exceeding the thickness of thepressure-responsive membrane switch. The foam pad is configured suchthat, upon it being compressed by application of pressure exceeding acertain threshold, it deforms so as to penetrate into the recess andactivates the pressure-responsive membrane switch.

Preferably, the spacer elements are integrally formed with the supportplate. The support plate and the spacer elements are preferably madefrom injection-molded plastic, although other materials may provesuitable.

The pressure-responsive membrane switch used in accordance with thefirst or second aspect of the invention advantageously comprises a firstcarrier film and a second carrier film spaced from each other by aspacer film, the spacer film having therein an opening defining a cell,the pressure-responsive membrane switch comprising at least twoelectrodes arranged in facing relationship with each other in the cellon the first and the second carrier film, respectively, in such a waythat they are brought closer together, possibly into contact with eachother, when pressure is applied on the pressure-responsive membraneswitch. When a contact between the electrodes on the first and secondcarrier film is established, one speaks of “activation” of the membraneswitch. The minimum amount of pressure at which the contact isestablished is called the “pressure threshold” or the “activationthreshold”.

A further aspect of the invention relates to a vehicle seat, comprisinga seat cushion supported by cushion-supporting springs and apressure-responsive seat occupancy sensor unit according to the firstaspect of the invention. The pressure-responsive seat occupancy sensorunit rests on the cushion-supporting springs and is applied by thecushion-supporting springs against the seat cushion.

Yet a further aspect of the invention relates to a vehicle seat,comprising a seat cushion supported by a cushion-supporting pan and apressure-responsive seat occupancy sensor unit in accordance with thesecond aspect of the invention. The pressure-responsive seat occupancysensor unit in this case rests on the cushion-supporting pan and isapplied by the cushion-supporting pan against the seat cushion.

When the seat is loaded (by an occupant), the seat foam is compressedand transfers a part of the pressure to the foam pad of the seatoccupancy sensor unit. In turn, the foam pad deforms and penetrates intothe recess. If the pressure transferred to the pressure-responsivemembrane switch exceeds the pressure threshold, the latter is activatedand the occupancy of the seat is recognized.

As will be appreciated, the sensitivity of the seat occupancy sensorunit depends on and may thus be adjusted by at least the followingparameters:

-   -   Height and hardness of the foam pad;    -   Height of the gap between the foam pad and the        pressure-responsive membrane switch;    -   Activation threshold of the membrane switch;    -   The size (diameter) of the recess in relation to the supported        area of the foam pad.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 is a cross sectional view of a pressure-responsive seat occupancysensor unit according to the first aspect of the invention;

FIG. 2 shows the pressure-responsive seat occupancy sensor unit of FIG.1 when the seat, which it is arranged in, is occupied;

FIG. 3 is a perspective view of the pressure-responsive seat occupancysensor unit of FIG. 1 without the foam pad;

FIG. 4 is a perspective view of the pressure-responsive seat occupancysensor unit of FIG. 1 wherein the foam pad is shown;

FIG. 5 is a cross sectional view of a pressure-responsive seat occupancysensor unit according to the second aspect of the invention;

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 to 4 show a pressure-responsive seat occupancy sensor unit 10for a vehicle seat according to a preferred embodiment of the firstaspect of invention. The occupancy sensor unit 10 comprises a supportplate 12 which is integrally formed with lateral bearing elements 14, bywhich the support plate is attached to the cushion-supporting springs 16of the seat. The bearing elements 14 define an upper surface 18 of theoccupancy sensor unit, from which upper surface 18 the top surface 20 ofthe support plate 12 is arranged recessed. A foam pad 22 is disposedbetween the bearing elements 14 on the top surface 20 of the supportplate 12. A recess 24 formed in the top surface 20 of the support plate12, underneath the foam pad 22, accommodates a pressure-responsivemembrane switch 26. The depth of the recess 24 exceeds the thickness(height) of the membrane switch 26.

The upper surface 28 of the foam pad 22 is substantially in alignmentwith the upper surface 18 of the occupancy sensor unit 10. Both surfacesare thus applied against the bottom side (B-surface) of the seat cushion30. When the seat is loaded (illustrated in FIG. 2 by arrow 32), theseat cushion transfers part of the resulting pressure onto the occupancysensing unit 10, in particular onto the foam pad 22. The mechanicalproperties of the foam pad 22 are chosen such that, when the foam pad 22is compressed by application of pressure exceeding a certain threshold,it deforms so as to penetrate into the recess 24 in the top surface ofthe support plate 12 and activates the pressure-responsive membraneswitch 26.

FIG. 3 shows the occupancy sensing unit 10 from a different perspective.The foam pad 22 and the seat cushion are not shown in FIG. 3 for sake ofclarity. The lateral bearing elements 14 rest upon thecushion-suspension mat formed by the springs 16 and the cross-ties 34.The support plate 12, which is in recess from the upper surface 18 ofthe occupancy sensing unit 10 carries a sensor device with two activeareas 36, each of which represents a pressure-responsive membrane switch26. Both switches are electrically linked to a connection tail, which isprotected by a hot-melt casing 38. The connection tail serves tointerface the sensor device with read-out electronics (such as e.g. acar's onboard computer). FIG. 4 shows the same perspective as FIG. 3,with the foam pad 22 in place.

FIG. 5 illustrates a preferred embodiment of a seat occupancy sensorunit 10′ according to a second variant of the invention, integrated intothe seating portion of a vehicle seat 40. The vehicle seat comprises aseat pan 42, which supports the seat cushion 30′. The occupancy sensorunit 10′ rests upon the seat pan 42.

The pressure-responsive seat occupancy sensor unit 10′ comprises asupport plate 12′ a plurality of spacer elements 14′ defining an uppersurface 18′ of the pressure-responsive seat occupancy sensor unit fromwhich upper surface 18′ the top surface of the support plate is arrangedrecessed from. A foam pad 22′ is disposed between the spacer elements14, carried by the support plate 12′. A recess 24′ formed in the topsurface of the support plate 12′, underneath the foam pad 22′,accommodates a pressure-responsive membrane switch 26′. The recess 24′has a depth exceeding the thickness of the membrane switch 26′. The foampad 22′ is configured such that, upon it being compressed by applicationof pressure exceeding a certain threshold, it deforms so as to penetrateinto the recess 24′ and activates the membrane switch 26′.

While specific embodiments have been described in detail, those skilledin the art will appreciate that various modifications and alternativesto those details could be developed in light of the overall teachings ofthe disclosure. Accordingly, the particular arrangements disclosed aremeant to be illustrative only and not limiting as to the scope of theinvention, which is to be given the full breadth of the appended claimsand any and all equivalents thereof.

The invention claimed is:
 1. A pressure-responsive seat occupancy sensorunit for detecting an occupancy state of a seat, comprising: a supportplate having a top surface and a bottom surface, a plurality of bearingelements for fixation of said support plate on seat cushion suspensionsprings, said bearing elements defining an upper surface of saidpressure-responsive seat occupancy sensor unit, wherein said top surfaceof said support plate is arranged recessed from said upper surface; afoam pad disposed between said bearing elements on said support plate; arecess formed in said top surface of said support plate, underneath saidfoam pad; and a pressure-responsive membrane switch arranged in saidrecess, wherein said recess has a depth exceeding the thickness of saidpressure-responsive membrane switch.
 2. The pressure-responsive seatoccupancy sensor unit as claimed in claim 1, wherein said bearingelements are integrally formed with said support plate.
 3. Thepressure-responsive seat occupancy sensor unit as claimed in claim 2,wherein said support plate and said bearing elements are made ofinjection-molded plastic.
 4. The pressure-responsive seat occupancysensor unit as claimed in claim 1, wherein said pressure-responsivemembrane switch comprises a first carrier film and a second carrier filmspaced from each other by a spacer film, said spacer film having thereinan opening defining a cell, said pressure-responsive membrane switchcomprising at least two electrodes arranged in facing relationship witheach other in said cell on said first and said second carrier film,respectively, in such a way that they are brought closer together,possibly into contact with each other, when pressure is applied on saidpressure-responsive membrane switch.
 5. The pressure-responsive seatoccupancy sensor unit as claimed in claim 1, wherein said foam pad isconfigured such that, upon it being compressed by application ofpressure exceeding a certain threshold, it deforms so as to penetrateinto said recess and activates said pressure-responsive membrane switch.6. A vehicle seat, comprising a seat cushion supported bycushion-supporting springs and a pressure-responsive seat occupancysensor unit, said pressure-responsive seat occupancy sensor unit,comprising: a support plate having a top surface and a bottom surface, aplurality of bearing elements for fixation of said support plate on seatcushion suspension springs, said bearing elements defining an uppersurface of said pressure-responsive seat occupancy sensor unit, whereinsaid top surface of said support plate is arranged recessed from saidupper surface; a foam pad disposed between said bearing elements on saidsupport plate; a recess formed in said top surface of said supportplate, underneath said foam pad; and a pressure-responsive membraneswitch arranged in said recess, wherein said recess has a depthexceeding the thickness of said pressure-responsive membrane switch andwherein said pressure-responsive seat occupancy sensor unit rests onsaid cushion-supporting springs and is applied by saidcushion-supporting springs against said seat cushion.
 7. Apressure-responsive seat occupancy sensor unit for detecting anoccupancy state of a seat, comprising: a support plate having a topsurface and a bottom surface, a plurality of spacer elements defining anupper surface of said pressure-responsive seat occupancy sensor unitfrom which upper surface said top surface of said support plate isarranged recessed from; a foam pad disposed between said spacerelements, carried by said support plate; a recess formed in said topsurface of said support plate, underneath said foam pad; and apressure-responsive membrane switch arranged in said recess, whereinsaid recess has a depth exceeding the thickness of saidpressure-responsive membrane switch.
 8. The pressure-responsive seatoccupancy sensor unit as claimed in claim 7, wherein said spacerelements are integrally formed with said support plate.
 9. Thepressure-responsive seat occupancy sensor unit as claimed in claim 8,wherein said support plate and said spacer elements are made ofinjection-molded plastic.
 10. The pressure-responsive seat occupancysensor unit as claimed in claim 7, wherein said pressure-responsivemembrane switch comprises a first carrier film and a second carrier filmspaced from each other by a spacer film, said spacer film having thereinan opening defining a cell, said pressure-responsive membrane switchcomprising at least two electrodes arranged in facing relationship witheach other in said cell on said first and said second carrier film,respectively, in such a way that they are brought closer together,possibly into contact with each other, when pressure is applied on saidpressure-responsive membrane switch.
 11. The pressure-responsive seatoccupancy sensor unit as claimed in claim 7, wherein said foam pad isconfigured such that, upon it being compressed by application ofpressure exceeding a certain threshold, it deforms so as to penetrateinto said recess and activates said pressure-responsive membrane switch.12. A vehicle seat, comprising a seat cushion supported by acushion-supporting pan and a pressure-responsive seat occupancy sensorunit, said pressure-responsive seat occupancy sensor unit comprising asupport plate having a top surface and a bottom surface, a plurality ofspacer elements defining an upper surface of said pressure-responsiveseat occupancy sensor unit from which upper surface said top surface ofsaid support plate is arranged recessed from; a foam pad disposedbetween said spacer elements, carried by said support plate; a recessformed in said top surface of said support plate, underneath said foampad; and a pressure-responsive membrane switch arranged in said recess,wherein said recess has a depth exceeding the thickness of saidpressure-responsive membrane switch and wherein said pressure-responsiveseat occupancy sensor unit rests on said cushion-supporting pan and isapplied by said cushion-supporting pan against said seat cushion.